Electron discharge tube comprising a luminescent screen



Feb 23, 1956 F. H. BITTER E1; AL 2,736,834

ELECTRON DISCHARGE TUBE COMPRISING A LUMINESCENT SCREEN Filed May 16,1952 INVENTORS. Ewvz [/EIZM/JNN BITTER By KARL Avausrlizsm v UnitedStates Patent 2 736 834 ELECTRON DlscHAfkGE TUBE COMPRISING ALUMINESCENT SCREEN Franz Hermann Bitter, Hamburg, and Karl AugustBisterfeld, Hamburg-Volksdorf, Germany, assignors to Hartford NationalBank and Trust Company, Hartford, Conn., as trustee Application May 16,1952, Serial No. 288,251 Claims priority, application Germany August 10,1951 3 Claims. (Cl. 313-1075) For the at least qualitative opticalindication, more particularly of the tuned position, preferably insilent tuning of wireless receivers, use is made of electron tubescomprising a luminescent screen, so-called tuning indicator tubes, whichindicate when the tuned position is optimum by the width of one or moreluminescent angles controlled as a function of a voltage correspondingto the mean high-frequency amplitude or by the length of a luminescentstrip, so-called thermometer-like indication.

The electron beam is in this case controlled by a control grid which iswound with a variable pitch of the grid wires, or by a control cylinder,Wehnelt cylinder, which is laterally slotted in the form of a wedge, orby control rods provided parallel to the cathode.

The anode is in most cases constituted by the luminescent screen itselfor is provided either in the form of one or more pins or in the form ofa small plate, preferably slotted, between the control system and theluminescent screen.

In known electron tubes comprising a luminescent screen and moreparticularly in tuning indicator tubes having a thermometer-likeindication, the disadvantage occurs that the indication has not the sameaccuracy, for example, with strong and weak transmitters. Consequently,two angular systems having different sensitivities are provided in thetuning indicator tube comprising luminescent sectors, which naturallyrequires a considerably greater exertion in assembling the tube and inthe wiring thereof.

Said disadvantages may be obviated and a regular clear indication withgreat and small control amplitudes is possible with little structuraland wiring-technical exertion in an electron tube comprising aluminescent screen and more particularly in a tuning indicator tubecomprising a thermometer-like indication in which a control electrodehaving a locally irregular control action is provided between cathodeand anode or luminescent screen if, according to the invention, thewhole luminescent screen or part thereof is provided in an inclinedposition with respect to the axis of the cathode. In this case, theluminescent screen may also serve as an anode. However, it isalternatively possible to utilise an anode which preferably has theshape of a slotted plate andas viewed in the direction of the electronray--to provide thereafter an auxiliary anode which serves as theluminescent screen and which preferably has the same potential as themain anode. According to a further embodiment of the invention, the mainanode and the luminescent screen may be made in one piece. By the deviceaccording to the invention it may be ensured that the indication is notlinear but that, for example, for the first half of the length of theluminescent strip of the control voltage for the whole length of thestrip is required. Such a characteristic, which is preferablylogarithmic, is particularly advantageous for use as a tuning indicatortube, since strong and weak transmitters thus provide a clearly visibleindication, that is to say, that the system cannot substantially beovercontrolled.

Such a device comprising a luminescent screen in an inclined positionfurthermore has the advantage that it is possible to'obtain acomparatively compact structure which may readily be incorporated evenin a small electron tube, for example, a Rimlock or a Noval tube, inwhich the cathode is preferably provided in an inclined position withrespect to the axis of the tube and the luminescent screen is wellvisible in a broad angle range of about about the axis of the tube bulb,while embodiments hitherto known have a small range of visibility only.The tube may in practice be given any desired characteristic line by theuse of a curved luminescent screen.

Furthermore, such electron tubes comprising a luminescent screenfrequently involve the disadvantage that at the beginning of theindication range, short luminescent strip, the brightness of theluminescent column is small, but greatly increases towards the end ofthe indication range, long luminescent strip, more particularly in thepart which luminesces first, the starting range. The viewing is thusvery detrimentally affected. This disadvantage may be obviated if insuch an electron tube, more particularly of the type in which anauxiliary anode is provided separately from the anode as the luminescentscreen, the Whole anode or part thereof occupies an inclined positionwith respect to the axis of the cathode. Substantially any desireddistribution of brightness and more particularly even distribution ofbrightness in the luminescent strip may be obtained if the anode is madecurved.

In order that the invention may be readily carried into effect, it willnow be described in greater detail with reference to the accompanyingdrawing in which:

Fig. 1 shows an elevational view of one form of tube in accordance withthe invention;

Fig. 2 is a perspective view of a part of the tube illustrated in Fig.1;

Fig. 3 shows a modification of the tube illustrated in Fig. 1.

Referring now to the drawing, between pins 1 and 2 provided in a glassbase 9 of a Rimlock tube is arranged an indirectly-heated cathode 3, ofwhich the filament leads are not shown. The cathode 3 is surrounded by agrid 4, which is wound with a continuously variable pitch and which isconnected in a conventional manner (not shown) to one of the contactpins. An anode 5, which comprises a longitudinal slot (Fig. 2) and whichis made in one piece with a strip-like, luminescent screen 6 of about 10mms. in width is connected electrically and mechanically to a contactpin 7. A small tube 8 secured to the upper end of the luminescent screen6 contains the greater material which is vaporised in known manner whenthe manufacture of the tube is completed.

According to the invention, the plane luminescent screen 6 occupies aninclined position of approximately 60 with respect to the axis of thecathode 3. The plate or accelerating anode 5 is likewise provided in aninclined position with respect to the axis of the cathode in order toensure a more satisfactory distribution of brightness in the luminescentcolumn. The anode and luminescent screen, 5 and 6, are in this casepreferably made in one piece.

Upon decrease of an initially high negative bias of grid 4, an electroncurrent will first fiow through the wide meshes of the grid to strikethrough the anode 5 the screen 6 which is coated with luminescentsubstance, so that its lower end luminesces first. In combination with asuitable choice of the variable pitch of grid 4, it may be ensured bybending, for example, the upper end 6' (Fig. 3) of the luminescentscreen that the absolute indication sensitivity in the upper part of theluminescent screen greatly decreases with respect to the sensitivity inthe lower part, so that with unvaried relative sensitivity anovercontrol is substantially avoided even with a considerable increasein grid bias.

What we claim is:

1. An electrode system for a tuning indicator tube, c0mprising'anelongated cathode having a given longitudinal axis, a wound gridelectrode surrounding and concentric with said cathode, said grid havinga variable winding pitch progressively decreasing in value toward oneend of the cathode, an accelerating anode having an aperture thereinspaced from said cathode and grid, said accelerating anode beinginclined at an acute angle with respect to the axis of the cathode, andan elongated luminescent screen facing said cathode and being disposedsubstantially on the side of said accelerating anode remote from saidcathode, said luminescent screen being aligned with the cathode and withsaid aperture in said anode, said luminescent screen being inclined atan acute angle with respect to said axis of said cathode different fromthe angle of inclination of said accelerationg anode with respect tosaid cathode, said luminescent screen being closer to the other end ofsaid cathode than to said one end.

2. An electrode system as claimed in claim 1 wherein the luminescentscreen is curved.

3. An electrode system as claimed in claim '1 wherein the acceleratinganode is mounted on and secured to said luminescent screen.

References Cited in the file of this patent UNITED STATES PATENTS

